Can this test distinguish Candida albicans from other yeast species?

No. KOH preparation reveals yeast morphology but does not speciate. If identification of Candida species or non-Candida fungi is required, fungal culture with identification is necessary.

Is a positive KOH yeast result always clinically significant?

Not necessarily. Many healthy individuals carry low numbers of yeast in the gut. A positive result must be correlated with symptoms, risk factors, and the remainder of the stool panel rather than treated on microscopy alone.

Should antifungal therapy be stopped before collecting the specimen?

Ideally, yes — systemic or oral antifungals can reduce yeast load and yield false-negative or underestimated results. Discuss with the ordering practitioner whether a wash-out period is feasible and safe.

How is the specimen collected for this test?

The patient collects stool at home using the Genova-supplied kit, sampling from multiple areas of the specimen into the preservative vial, then ships it per the kit instructions. Avoid contamination with urine or toilet water.

What does a negative result mean?

Negative or trace (1+) suggests minimal yeast burden and argues against significant intestinal fungal overgrowth. However, it does not exclude intermittent overgrowth, sampling error, or systemic candidiaemia, and should be interpreted with the clinical picture.

Is fasting required before stool collection?

No. The test does not require fasting, though practitioners may advise dietary consistency or avoidance of antifungals for a period before collection to improve accuracy.

How long does it take to receive results?

Results are typically available within 7–10 business days from specimen receipt at Genova Diagnostics, and may be longer if ordered as part of a comprehensive stool analysis panel.

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Add-On: KOH Preparation for Yeast

The KOH Preparation for Yeast is a microscopy-based add-on test performed on stool to detect and semi-quantify yeast organisms, typically Candida species. Potassium hydroxide clears debris and preserves fungal structures for direct visualisation of budding yeast, pseudohyphae, or true hyphae. Ordered alongside comprehensive stool analysis when intestinal fungal overgrowth is suspected.

Biomarkers

Stool

Sample

7–10 business days

Turnaround

Fasting

What is the KOH Yeast Prep test?

The KOH Preparation for Yeast is an add-on microscopy test performed on a stool specimen to detect and semi-quantify yeast organisms when intestinal fungal overgrowth is suspected. Potassium hydroxide digests mammalian cells and background material, leaving fungal structures intact for direct microscopic examination — a technique that is simple, rapid, and widely used in dermatological and mucosal mycology but less standardised in stool analysis. Practitioners order this add-on when a patient presents with chronic gastrointestinal symptoms — bloating, irregular bowel habit, or unexplained abdominal discomfort — in the context of risk factors such as recent or recurrent antimicrobial courses, high dietary sugar intake, immunosuppression, or prior antifungal treatment failure. Because the test is qualitative to semi-quantitative and does not replace fungal culture or speciation, it serves as an adjunct to comprehensive stool analysis, flagging the presence of yeast morphology to guide empirical antifungal therapy or prompt further mycological investigation.

What does the KOH Yeast Prep test measure?

KOH Yeast Prep(Potassium Hydroxide Preparation for Yeast Identification)

Range: Negative or minimal; grading scales vary by laboratory.Optimal: Negative or trace (1+); higher grades (2+ to 4+) suggest overgrowth, though no universal threshold defines clinical significance and correlation with symptoms is essential.Qualitative / Semi-quantitative (1+ to 4+)

Yeasts — predominantly Candida species and occasionally Saccharomyces or other opportunistic fungi — are part of the normal intestinal microbiota in low numbers, coexisting with commensal bacteria in a balanced ecosystem. Overgrowth occurs when antimicrobial therapy, dietary substrates high in simple sugars, immune compromise, or mucosal barrier disruption shifts the balance in favour of fungal proliferation. Potassium hydroxide clears cellular debris and rapidly dissolves human cells while preserving fungal structures, permitting direct microscopic visualisation of yeast forms and pseudohyphae. Unlike culture, KOH microscopy is a rapid point-of-care adjunct that confirms morphology but does not speciate or quantify viable organisms with precision.

The add-on KOH preparation provides a rapid qualitative or semi-quantitative assessment of yeast burden in a stool specimen, typically ordered alongside comprehensive digestive-stool analysis when fungal overgrowth is suspected. A positive result — budding yeast cells, pseudohyphae, or true hyphae — supports the hypothesis of intestinal yeast overgrowth and informs whether antifungal intervention is warranted. Because the test is morphology-based and does not culture, it may underestimate viable load if organisms are sparse or intermixed with debris, and it cannot distinguish Candida albicans from non-albicans species. Practitioners use the result in the clinical context of symptoms, risk factors, and the broader stool panel rather than as a stand-alone diagnostic.

Why is the KOH Yeast Prep test ordered?

Patients with chronic gastrointestinal symptoms and a history of recurrent or prolonged antibiotic courses that may have disrupted commensal flora
Evaluation of suspected intestinal Candida overgrowth in individuals with high simple-sugar diets, recurrent vaginal or oral thrush, or systemic candidiasis risk
Immunocompromised patients — including those with HIV, chemotherapy, or corticosteroid therapy — presenting with unexplained bloating, diarrhoea, or malabsorption
Follow-up assessment of antifungal therapy response in patients previously treated for documented fungal overgrowth
Functional-medicine contexts where a comprehensive digestive-stool analysis is ordered and yeast overgrowth is part of the differential diagnosis
Patients with refractory irritable-bowel-like symptoms in whom standard bacterial and parasitic evaluation has been unrevealing

Sample collection and turnaround

Sample type

Stool

Fasting required

Collection method

At-home collection kit

Turnaround

7–10 business days

Collection notes

Patient collects a stool specimen at home using the kit supplied by Genova Diagnostics, following the laboratory's instructions for sampling from multiple areas of the specimen and using the provided preservative vial or collection device. The specimen should be collected before starting or after discontinuing antifungal therapy where feasible. Ship promptly per kit instructions to maintain specimen integrity.

Specimen requirements

Stool specimen in Genova-supplied collection vial with preservative. Sample from multiple areas of the stool to improve detection of heterogeneously distributed yeast. Avoid contamination with urine or toilet water. Refrigerate until shipment if instructed; follow prepaid shipping return within the specified window.

What can affect KOH Yeast Prep results?

reducesAntifungal medication use before collection

Systemic or oral antifungals decrease viable yeast load, potentially yielding a false-negative or underestimated result; a wash-out period may be needed for accurate assessment.

variableInconsistent stool specimen or sampling from outer portion

Yeast distribution in stool is heterogeneous, so sampling error can miss pockets of overgrowth; collecting from multiple areas of the specimen improves sensitivity.

variableDelay in processing or inadequate preservative

Yeast cells can degenerate if the specimen is held at room temperature without preservative or processed after prolonged delay, reducing the clarity of morphology.

variableHigh dietary fibre or complex carbohydrate intake

Debris and plant material in the stool can obscure microscopic fields and make interpretation more difficult, though KOH clears much of this.

variableObserver experience and microscopy quality

KOH preparation is operator-dependent; artefacts, spores from dietary sources, and background debris can be mistaken for yeast, and low-grade positives may be missed by inexperienced readers.

What do KOH Yeast Prep results mean?

Elevated

Positive or high-grade (2+ to 4+) — Budding yeast, pseudohyphae, or true hyphae indicate overgrowth, most commonly Candida species. This supports empirical antifungal therapy (nystatin, fluconazole, or herbal agents), probiotic intervention, and dietary modification to reduce simple sugars. The result does not speciate, so if systemic infection or invasive disease is suspected, culture and susceptibility are required.

Normal

Negative or trace (1+) — Minimal or absent yeast forms. This argues against significant intestinal fungal overgrowth as the driver of symptoms, though it does not exclude intermittent overgrowth or deep-tissue candidiaemia, and it should be correlated with clinical presentation and the remainder of the stool panel.

Reduced

Not applicable. The test is presence/absence or graded; 'low' is reported as negative or trace (1+) and is not clinically significant.

Note: The KOH preparation is a qualitative to semi-quantitative morphology screen, not a quantitative culture. It cannot distinguish Candida albicans from non-albicans species, does not provide susceptibility data, and has not been standardised with validated diagnostic thresholds in stool. A negative result does not exclude fungal overgrowth if sampling was inadequate or antifungal therapy was recent. Positive results should be interpreted in the clinical context — many healthy individuals carry low numbers of yeast — and correlated with symptoms and risk factors rather than treated on the basis of microscopy alone.

Frequently asked questions

KOH microscopy provides a rapid morphological snapshot — budding yeast, pseudohyphae, or true hyphae — within hours, whereas culture requires days and quantifies viable organisms. KOH does not speciate or provide susceptibility data, so culture remains necessary if speciation or resistance testing is needed.

How to access the KOH Yeast Prep test

The KOH Yeast Prep reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.

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About this page

Published: October 7, 2026

Last reviewed: October 7, 2026

References:

Kumamoto CA. Inflammation and gastrointestinal Candida colonization. Curr Opin Microbiol. (2011)
Ramirez-Garcia A, et al. Candida albicans and cancer: Can this yeast induce cancer development or progression? Crit Rev Microbiol. (2016)
Pappas PG, et al. Clinical Practice Guideline for the Management of Candidiasis: 2016 Update by the Infectious Diseases Society of America. Clin Infect Dis. (2016)
Bacher P, et al. Human anti-fungal Th17 immunity and pathology rely on cross-reactivity against Candida albicans. Cell. (2019)

This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.